Arched strainer plate for plastic and like material

ABSTRACT

This invention relates to strainers and particularly to strainers for straining plastic, visco-elastic, or highly viscous, rubbery materials and more particularly to a strainer having an improved breaker plate.

United States Patent 1 91 Taylor et a1.

[54] ARCHED STRAINER PLATE FOR PLASTIC AND LIKE MATERIAL [75] Inventors: Challen E. Taylor, Waukegan; John 11. Stanley, Libertyville, both of 111.

[73] Assignee: The Goodyear Tire & Rubber Company, Akron, Ohio [22] Filed: Mar. 15, 1972 [21 Appl. No: 234,752

[52] US. Cl 259/193, 210/445, 210/446,

210/489, 210/492, 210/498, 210/499, 425/199 [51] Int. Cl 801d 35/28 [58] Field of Search 210/445-446,

[111 3,811,659 May 21, 1974 [56] References Cited UNITED STATES PATENTS 791,111 5/1905 DuPont 425/199 X 3,077,636 2/1963 Peters 425/197 2,488,595 11/1949 Henning 425/199 Primary ExaminerSamih N. Zaharna Assistant,EraminerF. F. Calvetti Attorney. Agent. or Firm-F. W. Brunnei'. R. 'S.

6 Claims, 3 Drawing Figures PATENTEUMMZ] m4 3,811,659

o o o 62 o o o 4 71 0 8 3 0 0 0 v I o o o o o o 0 0 o o o o o o o I o 0 0 o o o o o o o o o o o o 0 o o o o o 0 o o o o o o o o o 0 0 o 0 0 0 0 0 0 0 0 OOOOOOOOOOOOOOOO 0 0 0 0 0 0 0 3 080808080 0 0 0 0 0 o o o 0 o 0 03 C 0 0 0 1 0000 ii FIG. B

ARCIIED STRAINER PLATE FOR PLASTIC AND LIKE MATERIAL BACKGROUND OF THE INVENTION In the manufacture of articles such as hose, belting, tires, and other articles from plastic, or visco-elastic,

rubbery materials, it is common practice to use extrusion apparatus or other apparatus by which the material is pressurized and in which the pressure of such materials may reach 10,000 pounds per square inch or more. Such apparatus commonly includes means adapted to work the material by forcing it through mul tiple passages in a foraminous member commonly called a breaker plate to promote the plasticizing, softening, heating, or mixing, of the material. It is also common to employ such breaker plates together with other perforated or foraminous elements in order to remove from the material being worked unwanted particles of the material itself and of foreign material.

Heretofore, much difficulty has been experienced with such breaker plates not only because the initial pressure bearing upon them is high but because also such pressure tends to increase as the unwanted particles accumulate on the foraminous surfaces. A common solution to premature failure of breaker plates because of the excess pressure load has been to increase the thickness of the plates. Because the increased thickness of the breaker plate unavoidably increases the length of the passages through which the material travels, the pressure load on'the thicker breaker plate is also correspondingly increased. In the heretofore used flat breaker plates, the pressure of the material tends to bulge the plate outwardly, away from the pressure, with the result that maximum stresses become concentrated at the edges and at the center, the locations of maximum bending moments, and where failure of such plates commonly occurs. A further difficulty which has been experienced is that the outward bulging occurring in the breaker plate due to the high pressure load tends to deflect the edges of the plate so that escape passages are opened through which the material leaks around the edges of the plate rather than moving through the breaker plate passages.

SUMMARY OF THE INVENTION The present invention aims to overcome the foregoing and other difficulties experienced heretofore and has for a primary object the provision of an improved breaker plate. A further object is the provision of a breaker plate not subject to bulging and in which bending stresses are avoided. Another object is the provision of a breaker plate wherein the thickness of the plate and, accordingly, the length of the passages therethrough can be reduced relative to breaker plates heretofore used.

The foregoing as well as other objects and advantages made apparent hereinafter are accomplished in accordance with the invention by a strainer breaker plate having a spheroidal surface convex toward the main flow of material therethrough.

THE DRAWINGS A specific embodiment of the invention claimed is illustrated in the attached drawings wherein:

FIG. 1 is a longitudinal section view of apparatus embodying a strainer in accordance with the invention;

DETAILED DESCRIPTION In FIG. 1, means for pressurizing the material being worked is illustrated in the form of an extruder 10 having a cylindrical barrel 12 and an extruding screw 14, both of which are entirely conventional.

The strainer 20, including a plurality of strainer elements one of which is the breaker plate 22, is disposed across the delivery end of the extruder and there retained by the extruder head 24. Only a portion of the extruder head is shown inasmuch as there are a multitude of forms in common use and the head itself is not within the scope of the present-invention. The breaker plate 22 is supported at its circumferential edge in an annular recess 31 formed in the head 24. The annular ring portion 32 of the plate 22 is received in the counterbored recess 33 and bears on the face 34 of the extruder barrel 12 to seal the chamber 36 against escape of the material being worked otherwise than through the strainer. The strainer 20, the extruder head 24, and the ring 32 are secured conventionally to the extruder barrel.

FIGS. 2 and 3 illustrate in enlarged scale the strainer 20 and breaker plate 22. It will be appreciated that in working certain materials the breaker plate alone may suffice for the working of the material, when particulate matter is not to be removed, and that the nature and number of the elements of the strainer will be varied to suit the conditions of the working and of the specific materials being worked. In the illustrative embodiment the elements comprising the strainer 20 include, in addition to the breaker plate 22, a screen element in the form of a perforated plate 41. Alternatively, a woven wire mesh screen of suitable character, as is well known, can be substituted for the perforated plate 4]. Wire screen mesh can also be used a a third element (not shown) overlying the plate 41. In such alternative arrangements each element of the strainer must conform to the curvature of the next element, the combination being adapted to remove unwanted particles of the material being worked as well as of foreign materials.

In accordance with the invention, the breaker plate 22 is formed with a spheroidal surface 50 which has an axis of symmetry 52 aligned with the axis of the extruder barrel l2 and thus with the main direction of flow of the material being worked. In the present embodiment, the surface 50 of the breaker plate is spherical, having a radius of curvature of 4 inches and an effective diameter of 4% inches which is approximately equal to the inside diameter of the extruder barrel. The portion 32 of the breaker plate 22 radially outward of the effective diameter may take any suitable form for adaptation to a particular extruder or other pressurizing means.

The strainer 20 and particularly the breaker plate 22 forms an arch or dome which is convex in a direction opposed to the main flow of material therethrough. The pressure load applied therefore against the surface 50 by the material in the chamber 36 is communicated to the extruder head 24 as a direct force, outwardly toward the conical surface of the recess 31, as distinguished from the bending couple always associated with a flat plate breaker heretofore used. The bending moment tending to deflect the peripheral edge 30 of the plate 22 away from its support is negligible or nonexistent. Moreover, the stresses resulting within the breaker plate from the pressure exerted by the material normal to the surface 50 are, in a radial direction as well as in the thickness direction, entirely compressive. Even though circumferential stresses at the edge of the plate may be tensile, the latter are negligible due to the support of the ring 32 and of the head 24.

It will be appreciated that other spheroidal surfaces which can be generated by rotating any one of numerous classical curves about the axis of symmetry 52 can be used. For example, the surface 50 may be that of a paraboloid or of an ellipsoid. The significant characteristic of the curve chosen to generate the surface of the breaker plate is that the surface curvature is continuous without points of inflection or abrupt changes in curvature. The peripheral or circumferential edge 30 of the plate 22 can be conical, as is shown, or cylindrical if desired, the recess 31 being conformed to the surface 30 of the ring 32 both to support the plate 22. The ring is urged strongly against the surface 34 to prevent escape of material. If desired, the ring 32 and plate 22 can be joined together as by brazing but in the presently preferred embodiment illustrated in FIG. 1, the plate 22 and the ring 32 are formed as a unit of an integral piece of material such as steel.

In the breaker plate 22, a multiplicity of passages 60 extend therethrough parallel to the axis 52. Altematively, the passages 60 can extend normal to the surface 50, and are drilled holes approximately 0.34 inch in diameter, the thickness of the plate being 0.50 inch. The transverse dimension or diameter of each passage 60 is selected to suit the particular material being worked and may, for commonly worked materials, range from 95 to 3 times the thickness of the plate. The size or sizes of the passages may differ widely from the stated range for certain materials. The thickness of the plate is about -12 percent of the effective diameter or span. A thickness of from 5-15 percent of the effective diameter is usually satisfactory. In the breaker plate 22, the sum of the open areas of the passages 60 is 56 percent of the total effective area. The open area selected may range from 18 percent to as much as 60 percent depending upon the particular service for which the plate is intended. The height of the spheroidal surface relative to the plane of its perimeter is, in the breaker plate 22, about N6 of the effective diameter and may range from 5 percent to about 45 percent of the effective diameter depending on the particular service for the breaker plate.

The term, open area, as used herein will be understood to mean the net minimum area for flow of material through the breaker plate, and the sum of the areas of the passages at their least diameters in the plate, referred to the total effective area, which is the total area defined by the effective diameter of the plate across the barrel 12.

According to the invention, and contrary to the practice usual heretofore, the passages 60 are bell-mouthed at the entrances thereinto and decrease in diameter in the direction of flow of the material therethrough. At the surface 50 therefore the dimensions of the passages 60 are enlarged, by flaring, chamfering or countersinking each hole or passage 60 to a transverse dimension or diameter of 0.48 inch in the plate 22. The land area of the surface 50 on which the plate 41 is supported is thereby further reduced with respect to the open area. The transverse dimension or diameter of the passages at the surface 50 is selected according to the strength of the element, in particular the perforated plate 41, supported thereon. Such land area in contact with the overlying plate 41 masks and blocks a portion of the holes 62. Because of the increased stiffness of the arched breaker plate 22 of the invention, an additional element exemplified by the screen plate 41 can be of thinner material and with smaller holes. The following comparison with be illustrative of the advantage.

A flat breaker plate representative of the prior art would have, as an example, an array of holes 11/32 inch in diameter, spaced 7/ 16 inch on centers along 3 sets of parallel lines intersecting at which arrangement yields an open area of 56 percent. An additional element, commonly of perforated plate for screening would be used, but enlargement of the holes at the entrance end could not be tolerated because of the resulting reduction in strength. The perforated plate would of necessity be thicker and would have, as an example, a staggered array of 5/32 inch diameter holes spaced 3/16 inch on centers to give an open area of 63 percent. In combination, resistance to flow of material through both the perforated plate and the flat breaker plate would be proportional to the area of the former not masked by the land area of the latter, or about 35 percent.

On the other hand, an arched breaker plate according to the invention and illustrated by the plate 22, can without sacrifice of strength and service life, have the holes or passages 60 enlarged at the support surface 50, in the plate 22, 7/16 inch. The gross area of entrance to the passages 60 is thus increased to about 91 percent. The screening element which can now also be thinner, illustrated by the perforated plate 41 herein, has a similar arrangement of holes, the same being, however, 0.040 inch holes spaced 0.062 inch on centers in each of the 3l20 directions. Thus, the screen plate 41 has an open area of 37 percent. The resistance to flow of material through the combination of breaker 22 and plate 41, is proportional as before to the product: 91 percent of 37 percent, or about 35 percent.

By the invention a significant advantage is gained in the working of the material and finer straining because of the smaller holes and with greatly increased service life for the strainer, without increased power consumption with respect to the prior art strainer and flat breaker plate.

In the present embodiment, the strainer 20 includes, in addition to the breaker plate 22, the previously mentioned perforated plate 41, which is 0.030 inch in thickness having 0.040 inch diameter holes 62 spaced 0.062 inch center-to-center in staggered or equiangular array and serves as the screen element.

The operation of the extruder or other pressurizing means is entirely conventional. Numerous advantages, however, are obtained through the use of breaker plate 22 and strainer 20 in accordance with the invention. The breaker plate provides greater open area, through which the material is moved, at least proportional to the difference between the area of the spheriod and the area of the conventional flat breaker plate having the same effective diameter. The same amount or degree of working of the material can be achieved with less energy input; or the working can be increased without increase in the energy expended. Because of the greater strength of the arched breaker plate 22, the plate may be thinner than the heretofore conventional flat breaker plate and the resistance of flow due to the length of the passages is correspondingly reduced. The unwanted particles continue during operation to accumulate on the surface of the strainer and progressively to blind or clog the passages; however, because of the increased available area of the strainer according to the present invention it can be operated over longer periods before it becomes necessary to clean or replace the first screening element.

Because of the absence of the heretofore common severe bending of the conventional breaker plate, the breaker plate according to the present invention minimizes .or completely eliminates the tendency for the material being worked to escape outwardly around the mounting of the breaker plate.

Because the force exerted, by the material being worked, on the arched strainer and breaker plate 22 is communicated radially and axially outwardly to the extruder head 24, no bending couple tending to turn or rotate the ring 32 out of its plane of contact with the extruder face 34 can exist. Further, because of the absence of bending, the breaker plate can be formed of metal of higher hardness and greater rigidity which not only provides a breaker plate of greater strength but of greater wear resistance.

The term working as used herein is to be understood as including extruding, mixing, warming, plasticizing, pelleting, straining and similar operations employing pressurizing means such as conventional screw extruders, ram extruders, or screw pumps. Various materials subjected to such working include, but are not limited to, compounds of natural and/or synthetic rubber, compounds commonly known as plastics, and mixtures of rubber-like materials, of resins, of polymers, and waxes. Such materials have in common flow properties characterized as highly viscous, visco-elastic, pseudoplastic, or plastic.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art thatvarious changes and modifications may be made therein without departing from the spirit or scope of the invention.

We claim:

1. A strainer in combination with a screw extruder for working an uncured, curable rubber compound, wherein said strainer comprises a breaker plate having a multiplicity of passages therethrough and a spheroidal surface fixedly disposed transversely of the outlet of said extruder with its axis of symmetry aligned with the screw axis of said extruder and said surface convex toward said screw, said passages being convergent in the direction of flow of said compound therethrough; and a screen element of like spheroidal curvature disposed continuously on and supported by said spheroidal surface of said plate, said passages being flared to provide support area for supporting said screen element, said support area being engageable in supporting contact with said screen element over an area of less than about 12 percent of said spheroidal surface.

2. A strainer as claimed in claim I, wherein the length of said passages in the direction of flow of said material is less than the maximum diameters of said passages.

3. A strainer as claimed in claim 1, the sum of the open areas of said passages is in the range of 18 to 60 percent of the area of said breaker plate which area is exposed to contact with said compound.

4. A strainer as claimed in claim ll, wherein the transverse dimension of each said passage is in the range of 3 times to 1% times the thickness of said breaker plate, said thickness being measured in the direction of flow of said compound therethrough.

5. A strainer as claimed in claim 1, wherein said thickness is in the range of 5 to 15 percent of the diameter of the area of said breaker plate exposed to contact with said compound.

6. A strainer as claimed in claim 1, wherein the height of said spheroidal surface relative to the plane of the perimeter of said breaker plate exposed to contact with said compound is in the range of 5 to 45 percent of the diameter of said plate. 

1. A strainer in combination with a screw extruder for working an uncured, curable rubber compound, wherein said strainer comprises a breaker plate having a multiplicity of passages therethrough and a spheroidal surface fixedly disposed transversely of the outlet of said extruder with its axis of symmetry aligned with the screw axis of said extruder and said surface convex toward said screw, said passages being convergent in the direction of flow of said compound therethrough; and a screen element of like spheroidal curvature disposed continuously on and supported by said spheroidal surface of said plate, said passages being flared to provide support area for supporting said screen element, said support area being engageable in supporting contact with said screen element over an area of less than about 12 percent of said spheroidal surface.
 2. A strainer as claimed in claim 1, wherein the length of said passages in the direction of flow of said material is less than the maximum diameters of said passages.
 3. A strainer as claimed in claim 1, the sum of the open areas of said passages is in the range of 18 to 60 percent of the area of said breaker plate which area is exposed to contact with said compound.
 4. A strainer as claimed in claim 1, wherein the transverse dimension of each said passage is in the range of 3 times to 1/2 times the thickness of said breaker plate, said thickness being measured in the direction of flow of said compound therethrough.
 5. A strainer as claimed in claim 1, wherein said thickness is in the range of 5 to 15 percent of the diameter of the area of said breaker plate exposed to contact with said compound.
 6. A strainer as claimed in claim 1, wherein the height of said spheroidal surface relative to the plane of the perimeter of said breaker plate exposed to contact with said compound is in the range of 5 to 45 percent of the diameter of said plate. 